5. PROGRAM EVALUATION (continued)

5.3.3 Speed Results

Sweetwater received intensive education and enforcement spurred by the efforts of a vocal and active neighborhood association. In addition, the Tyregrip™ material was installed prior to Wave 5 of measurement. Three waves of speed measurement in total were collected (Waves 1, 4 and 5). The results are shown in Table 65 and Figure 13.

Table 65. Phoenix – Sweetwater Speed Results

The Sweetwater results show almost a 50-percent reduction in the number of drivers going 7 mph or more over the limit. The reduction is largest in the last wave. The mean speed of the speeders also was reduced markedly as well as statistically significantly in both post waves when compared with the Wave 1 baseline. The reduction in the mean of speeders from 8.017 mph in Wave 4 to 7.634 mph in Wave 5 is also statistically significant (p<.001).

It should be noted that across the three waves of measurement the shift in speeds is largest to the lowest category (under the speed limit). This category more than doubles from Wave 1 to Wave 4 and is still more than double in Wave 5. At the same time, the intermediate category of people going less than 7 mph above the limit goes from 28.8 percent to 42.3 percent , an increase of 46.9 percent . Thus, the distribution shifts from the 7+ miles over the limit category to the two lower class intervals.

Figure 13. Speed Classes on Phoenix – Sweetwater

The mean of speeders shows continued improvement from Wave 4 to Wave 5. This suggests that the Tyregrip™ installation may have yielded a further moderation in the most aberrant speeds even though the mean speed rose slightly. Since there was only a single wave of measurement after the appearance of the Tyregrip™, no inference can be drawn concerning its long-term effectiveness.

The data for Sweetwater show a drop in traffic volume of 16.5 percent from Wave 1 to Wave 4. This volume reduction increases slightly from Wave 4 to Wave 5. This could be indicative of a small diversion of traffic to other parallel through streets. This is consistent with the opinion of the neighborhood association members who felt that many of the speeders were people cutting through the neighborhood on east/west trips. It is also supported by the police stop data shown previously in Table 23 which indicated that Sweetwater had the lowest percentage in Phoenix of people stopped who lived in or near the neighborhood. If there was a diversion, however, it cannot explain the marked reduction in those traveling 7+ miles over the limit. This number dropped by 8,606 between Wave 1 and Wave 5 while the total sample only decreased by only 4,862 vehicles.